Question

A person stands between two high walls d metres apart. He stands 400m from the nearer wall. He blows a whistle and hears two echoes, the first one after 2.5 seconds and the second one 2 seconds later. Determine:

1. The speed of sound in the air. 
2. The value of d

Answer 1

1. v = 2d = 2×400
          t        2.5
     =320ms⁻¹
2. v = 2d 
          t 
   d = vt = 320(2.5+4.5)
          2             2
      =1120m
   OR
   d − 400 = 320 × 4.5
                          2
   d = 720+400
      =1120m